I have personally learned all these topics from the Competitive Programmer's Handbook and parallelly solved the questions on the cses problemset. I would recommend these for you as well.

It might not be the best time to tackle these intermediate topics yet. Instead, focus on learning and practicing foundational concepts like sliding window, binary search, the two-pointer technique, prefix sums, and priority queues. However, if you still want to push ahead with intermediate material, you can refer to the USACO Guide for structured resources. They Provide good tutorial and Problems also.

what if you start solving 800 problems instead.